The Summer Triangle is an astronomical asterism

Asterism (astronomy)

In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...

 involving an imaginary triangle drawn on the northern hemisphere's celestial sphere

Celestial sphere

In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...

, with its defining vertices at Altair, Deneb

Deneb

Deneb is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars...

, and Vega

Vega

Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...

, being the brightest stars in the three constellations of Aquila

Aquila (constellation)

Aquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....

, Cygnus

Cygnus (constellation)

Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...

, and Lyra

Lyra

Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...

.

The English term was popularized by British astronomer Sir Patrick Moore in the 1950s, although he did not invent it. Austrian astronomer Oswald Thomas

Oswald Thomas

Oswald Thomas , was a German astronomer and a protagonist of the popularization of astronomy in Germany and Austria.-Career:...

 described these stars as "Grosses Dreieck" (Great Triangle) in the late 1920s and "Sommerliches Dreieck" (Summerly Triangle) in 1934. The asterism was remarked upon by J. J. Littrow

Joseph Johann Littrow

Joseph Johann von Littrow was an Austrian astronomer. In 1837, he was ennobled with the title Joseph Johann Edler von Littrow. He was the father of Karl Ludwig Edler von Littrow and the mentor of the mathematician Nikolai Brashman...

, who described it as the "conspicuous triangle" in the text of his atlas (1866), and Bode

Johann Elert Bode

Johann Elert Bode was a German astronomer known for his reformulation and popularization of the Titius-Bode law. Bode determined the orbit of Uranus and suggested the planet's name.-Biography:...

 connected the stars in a map in a book in 1816, although without label.

Near midnight the Summer Triangle lies virtually overhead at mid-northern latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s during the summer months, but can also be seen during spring

Spring (season)

Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...

 in the early morning. In the autumn

Autumn

Autumn is one of the four temperate seasons. Autumn marks the transition from summer into winter usually in September or March when the arrival of night becomes noticeably earlier....

 the summer triangle is visible in the evening well until November. From the southern hemisphere

Southern Hemisphere

The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

 it appears upside down and low in the sky during the winter

Winter

Winter is the coldest season of the year in temperate climates, between autumn and spring. At the winter solstice, the days are shortest and the nights are longest, with days lengthening as the season progresses after the solstice.-Meteorology:...

 months. "Northern Triangle" is a more neutral alternative.

The stars of the Summer Triangle

Name	Constellation	Apparent magnitude Apparent magnitude The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...	Luminosity (× solar)	Spectral type Stellar classification In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...	Distance (light years)
Vega Vega Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...	Lyra Lyra Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...	0.03	52	A0	25
Deneb Deneb Deneb is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars...	Cygnus Cygnus (constellation) Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...	1.25	70000	A2	1550
Altair	Aquila Aquila (constellation) Aquila is a stellar constellation. Its name is Latin for 'eagle' and it is commonly represented as such. In mythology, Aquila was owned by the Roman god Jupiter and performed many tasks for him....	0.77	10	A7	16.6

External links

• Summer Triangle at Basic Celestial Phenomena by Kerry Magruder
• Summer Triangle at The Astronomy Net
• Summer Triangle at DavidDarling.info
• Summer Triangle at Astronomy Picture of the Day